1. Field of the Invention
The invention relates to an AIS ship's transceiver that is provided for installation on a ship in order to be able to send and receive AIS radio signals containing ship data, having an AIS radio transmission unit that is designed to send radio signals of a first AIS radio signal type that contain ship data, wherein the AIS radio signals of the first AIS radio signal type are provided for the interchange of ship data from the ships among one another, and that is designed to send AIS radio signals of a second AIS radio signal type that contain ship data, wherein the AIS radio signals of the second AIS radio signal type are provided for reception by a satellite and for transmission of the ship data that the AIS radio signals of the second AIS radio signal type contain to a ground station by means of the satellite, and having an AIS radio reception unit that is designed to receive AIS radio signals of the first AIS radio signal type that contain ship data and that have been emitted by AIS ship's transceivers on adjacent ships.
The invention likewise relates to a method for the sending and receiving of AIS radio signals that contain ship data by such an AIS ship's transceiver therefor.
2. Background Description
Today, the monitoring of shipping traffic, which is increasing worldwide, is based predominantly on radar monitoring, radio telephony and on the use of AIS (Automatic Identification System). Since the year 2000, AIS has been stipulated by the International Maritime Organization (IMO) as a binding standard in order to increase the safety of international shipping traffic. This locally bounded radio system is used for the interchange of navigation data and other ship data that are intended to allow ships to obtain a comprehensive overview of the adjacent shipping traffic. The primary aim in this case is to prevent collision between ships.
An AIS ship's transceiver arranged on the ships is used to emit AIS radio signals that the relevant ship data, such as navigation data, alternately on two channels in the VHF marine radio range, namely firstly on 161.975 MHz and secondly on 162.025 MHz, using the broadcast method. In this case, the individual AIS radio signals are emitted in fixed time columns, the use of which is coordinated independently by the relevant subscribers of an AIS radio cell, known as SOTDMA (Self Organizing Time Division Multiple Access). Therefore, there are just 2250 timeslots per minute available for transmitting data to the individual subscribers.
The AIS ship's transceiver installed on board can be used to receive the radio signals emitted by the other ships, with the ship data that the AIS radio signals contain then being able to be extracted. The reception of the ship data from various ships in the surroundings of a ship can therefore be used to derive an overview of the adjacent shipping traffic or of the adjacent ships, which means that a ship is able, by way of example, to establish the direction in which and the speed at which adjacent ships that are not directly visible, for example on account of poor visibility, are traveling. It is therefore possible to avoid collisions and to produce a substantially improved, albeit locally bounded, picture of the situation.
On account of the VHF frequency band used, the radio range of AIS from ship to ship corresponds to approximately 40 to 60 km, which corresponds to a little more than the usual range of vision on the high sea. Coastal stations can cover a radius of up to 100 km as a result of their relatively high position. On account of the limited range and also the SOTDMA transmission protocol used, ships that are able to see and receive one another form an AIS radio cell within which the subscribers can send and receive without collision.
Hence, the AIS is merely a local radio system that, although it provides sufficient timeslot capacity for a ship on the high sea, is unsuitable for a worldwide, in particular satellite-based, survey of shipping traffic, since the coverage of a satellite includes many individual AIS radio cells. For shipping companies, the maritime organizations or Ministries of the Environment, however, a realtime survey of the AIS shipping data arising worldwide would be of great interest in order to counter illegal machinations on the high sea too, in particular.
By way of example, the subsequently published DE 10 2011 113 152 A1 thus discloses a global ship monitoring system that can be used to monitor ships in shipping traffic on the high sea centrally. To this end, commercial aircraft have AIS reception units that, on their flight route, receive the AIS radio signals emitted by the ships and transmit them for further processing to a ground station. This allows almost uninterrupted coverage and monitoring to be achieved particularly on much-used routes.
In the most recent past, attempts have been made to arrange AIS reception antennas on satellites so as to be able to receive the AIS radio signals emitted worldwide using a satellite system. By way of example, US 2008/0086267 A1 thus discloses a satellite-based system in which an AIS reception unit is arranged on the satellites in order to be able to receive the AIS radio signals emitted by the ships. The AIS information that the AIS radio signals contain is forwarded to a control center so as to obtain global monitoring of the shipping traffic. Such a satellite system can therefore be used to achieve uninterrupted monitoring even in remote regions.
Western industrial nations, in particular, require the introduction of checking of maritime traffic from space in the course of their fight against terrorism. However, satellite-based monitoring systems of this kind have the substantial disadvantage in respect of AIS radio signals in highly frequented maritime areas that it is no longer possible to detect ships with sufficient precision. On account of the extreme altitude of a satellite, a reception region with a diameter of between approximately 5000 and 6000 km is produced. Since the AIS as a local radio system is naturally organized into individual radio cells that all send on the same frequency band, such a large reception radius results in the reception of a multiplicity of radio cells having an identical transmission frequency and timeslots, however, which means that AIS radio signals from different AIS radio cells overlap and normal data processing is no longer possible. Precisely on highly frequented shipping routes or in the proximity of harbors and coasts, the reception region of the satellite covers such a large number of ships that sufficiently secure monitoring is no longer possible on account of the signal collisions.
In order to overcome this problem, two additional VHF channels for satellite-assisted monitoring using AIS radio signals will be provided in future in addition to the already existing AIS frequencies (AIS1: 161.975 MHz; AIS2: 162.025 MHz). To this end, specifically the channels on 156.775 MHz (AIS3) and 156.875 (AIS4) are intended to be allocated for communication for the purpose of receiving AIS radio signals from space by satellite. The background to the introduction of the additional satellite AIS (SAT-AIS) frequencies is the obtainment of as complete a maritime picture of the situation as possible using SAT-AIS on the high sea away from coastal regions. This is currently not possible with AIS1 and AIS2 alone for the reasons cited above (interference).
According to the definition of the ITU (ITU-R-M-1371-4), AIS3 and AIS4 radio signals are automatically switched off by the ship when the ships are in the communication range of what are known as AIS ground stations (AIS base stations), which are usually installed on the coast. When a ship receives a “Base Station Report” (Message 4), emitted by an AIS ground station, with the request to shut down SAT-AIS (control bit for “Transmission control for longrange broadcast message”), the AIS ship's transceiver installed on the ship deactivates the emission of the AIS3/AIS4 radio signals for satellite-assisted monitoring. The effect intended to be achieved by this is that in coastal regions, which usually have a high level of traffic on account of the concentration of the shipping traffic, no AIS3/AIS4 radio signals are intended to be emitted so as not to interfere with the satellite reception on account of a large number of radio signals that may overlap one another. The monitoring is then effected by means of the AIS ground stations. If the ship is outside the communication range of an AIS ground station, the emission of the AIS3/AIS4 radio signals for satellite-assisted monitoring is automatically switched on again by the ship.
However, there is currently only a very small number of such AIS ground stations worldwide, with usually only pure AIS reception stations being operated in the area close to the coast, which AIS reception stations, although sufficient for monitoring ships close to the coast, are unable to emit an AIS ground station message on account of the lack of transmission unit, and therefore the AIS ship's transceiver continues to emit AIS3/AIS4 radio signals in the communication range of AIS ground reception units even in proximity to the coast. As a result, in the absence of an AIS ground station, the problem arises in proximity to the coast that the ships continue to emit their AIS radio signals for satellite-assisted monitoring on the AIS3/AIS4 frequencies, however, which means that collisions occur in the case of satellites that these on account of the large number of radio signals, as a result of which it is no longer possible to safeguard adequate monitoring of the shipping traffic even with the newly introduced frequencies.